More specifically, the invention relates to a mounting system for at least one shaft, the shaft extending in a vertical direction, the mounting system comprising                a housing adapted to enclose the shaft with a radial clearance and        a moving carriage that can be moved between a blocking position and an unblocking position,        at least a jaw movable between an immobilization position and a release position,        
the jaw being driven by the moving carriage to be in the immobilization position when the moving carriage is in the unblocking position and in the release position when the moving carriage is in the blocking position, the jaw being adapted to apply, when it is in the immobilization position, a clamping force to the shaft in a clamping direction perpendicular to the vertical direction, so that the shaft is supported on the housing.
Document EP 1 602 527 describes an example of a mounting system for a headrest on a seat that includes the features mentioned above and allows the retraction of the headrest simply under gravity. In order to allow the descent of the headrest under gravity, it is necessary for the shafts to be free in their move and for the housing to thus enclose them with a radial clearance. This radial clearance lets the shafts free to vibrate inside the housing, which causes rattle and vibration sounds unpleasant to the user when the motor vehicle is moving. In order to limit these disadvantages, the mounting system detailed in document EP1 602 527 presents a clamping device for the shafts adapted to exert a force that places them in support against the housing walls.
In order to allow the user to easily adjust the height of the headrest, the force exerted by the clamping device on the shafts is limited so as to allow the shafts to slide in the vertical direction when the user exerts a force on the headrest.